The invention relates to a luminaire for mixing light from different color LEDs, in particular to produce white light.
The standard light source for small to moderate size narrow beam lighting for accent lighting and general illumination is the incandescent/halogen bulb, such as a PAR (parabolic aluminized reflector) lamp. These sources are compact and versatile, but they are not very efficient. A given lamp operates at a given color temperature for a fixed power, and while they are dimmable, the color temperature shifts with applied power according to the blackbody law, which may or may not be the variation that the user desires.
An array of LEDs in each of a plurality of colors offers the possibility of creating a luminaire in which the color temperature may be controlled at any power level, thereby enabling a lamp which is dimmable and emits a uniformly white light at any power level.
The English language abstract of JP-A-06 237 017 discloses a polychromatic light emitting diode lamp having a 3.times.3 array of light emitting diodes of two types, a first type having elements for emitting red light and blue light, and a second type having elements for emitting red light and green light. The stated object is to mix colors so that the mixed color would be recognized as the same color in any direction, but there are no optical provisions to facilitate mixing. It is simply a two-dimensional array of LEDs in a lamp case filled with resin, which would do little more than provide some diffusion.
U.S. application Ser. No. 09/277,645, filed Mar. 26, 1999, discloses a luminaire having a reflector which mixes light from a multi-color array of LED's. The array is arranged in the entrance aperture of a reflecting tube which preferably flares outward toward the exit aperture, like a horn, and has a square or other non-round cross-section. The object is to produce a collimated beam of white light in the manner of a spotlight. However the design is only appropriate for beams greater than about 2.times.15 degrees divergence.
The English language abstract of JP-A-01 143 367 discloses an arrangement employing a dichroic filter for mixing light from two LED light sources emitting light beams at right angles to each other. The filter is arranged at 45 degrees to each beam, and is fully transmissive to a red beam and fully reflective to a yellow beam. This offers three color possibilities for the output beam, depending upon which LEDs are powered. However there is no suggestion of using beam splitters to mix the light, mixing light of more than two colors, or producing white light.